The present invention relates to the field of power distribution, and more particularly to an apparatus for improving power distribution in a coaxial cable amplifier used to distribute video signals containing radio frequency (RF) power.
To distribute video signals for cable and satellite television broadcast, as well as video conferencing signals, two forms of electrical signal energy are used. A radio frequency (RF) signal to carry the video content information, and a low frequency (60 Hz) 60 Volt power signal that is used to provide power for downstream components (i.e., line extenders and amplifiers). The low frequency power signal provides electrical power to the downstream devices, allowing the RF signal to be distributed to a number of different receiving points.
Conventionally, in video signal distribution systems, video information received from an upstream video source is converted from an optical signal to the RF signal to aid in the signal's propagation. An optical-to-RF conversion device, such as a Broadband Telecommunication Node (BTN), receives the optical signal, converts it to an RF signal, and distributes the converted signal between a number of output ports.
FIG. 1 is a block diagram of a power distribution path in a BTN device 100 for converting optical video signal to an RF signal and distributing the converted signal. BTN device 100 includes a number of output ports (1, 3, 4, and OUT), a power input port 2, a signal input port (not shown), and a power supply 110. BTN device 100 further includes several fuses 112, 114, 116, 118, 120, and 122 that provide current protection for the power supply and the output signal lines of BTN device 100. Power supply 110 is a 1.5 amp internal supply that allows operation of BTN device 100 and distribution of the RF power to the output ports of BTN device 100.
FIG. 2 is a block diagram showing a low-power configuration of a video signal distribution system 200 using a BTN device 100 consistent with FIG. 1. In FIG. 2, BTN device 100 drives four lightly loaded outbound coaxial cable lines A, B, C, and D. Each coaxial cable has a load of about 3 amps in this low-power configuration and individually act as an output source for ports 1, 3, 4, and OUT. Port 2 acts as an input power port that is supplied with power from primary power module 210. In this configuration, power module 210 is a 15 amp supply that operates at a designed maximum of 13.5 amps. Each cable line A, B, C, and D draws approximately 3 amps and the BTN device 100 requires 1.5 amps. The configuration depicted in FIG. 2 is rarely achieved, however, because the loads connected to the cable lines rarely draw the same current and additional electrical power is often needed to drive the downstream devices coupled to BTN device 100.
FIG. 3 is a block diagram showing a typical configuration of a video signal distribution system 300 using BTN device 100 consistent with that shown in FIG. 1. In this configuration, coaxial cable lines A, B, C, and D draw a total of 20 amps, with an unbalanced current load distribution of 3, 5, 5, and 7, respectively. Cable lines A and B are connected together via fuses internal to BTN device 100 (i.e., as seen in FIG. 1) and are powered by power module 210, a 15 amp power supply that provides BTN device 100 with 9.5 amps via input port 2.
In this configuration and in order to accommodate the unbalanced loads drawn by cable lines A, B, C, and D, power to at least two of the output ports must be blocked and additional power needs to be inserted directly into the blocked lines to operate connected downstream loads. In FIG. 3, power inserters 230 and 232 are coupled to output ports OUT and 4, respectively, of BTN device 100. To operate power inserters 230 and 232, an auxiliary power module 220 is required for the electrical power source. In this configuration, the power for inserters 230 and 232 is supplied from power module 220 via a third power inserter 234.
Power inserters 232 and 230 provide the electrical power (i.e., 60 Volts) necessary to operate the downstream devices (i.e., amplifiers, etc.) previously described. These inserters, however, require additional connections and couplings to the cable lines. The couplings and additional connections often degrade the output signal and ultimately result in a weaker or less stable signal at an end receiving apparatus. This signal degradation or "insertion loss" is a significant problem when additional connections and lines are added to the distribution system because the final video signal received will be of a lower quality and strength.
FIG. 4 is a block diagram of an alternative configuration for distributing video signals using power line inserters. In this configuration, a fourth power inserter 236 is coupled to input port 1 and power module 210 and all the outbound cable lines have a balanced load requirement of 5 amps. Inserter 236 is added to ensure that the 5 amps supplied to port 1 is output through port 3. Again, BTN device 100 draws 1.5 amps from power module 210 which causes power module 210 to function at 11.5 amps or 77 percent of its rated operating capacity. Auxiliary power module 220 delivers 10 amps or 67 percent of its rated value.
The example depicted in FIG. 4 also introduces reliability problems into the distribution system. With the addition of the power inserter 236 into the system the electrical power source is located on the wrong side of the internal line protection fuse 116 shown in FIG. 1. If, for example, cable B is shorted, the fault will cause fuse 116, coupled to port 1, to open or a fuse within inserter 236 to blow. With either occurrence, the power to internal power supply 110 is interrupted because the power signal from primary power module 210 is blocked from entering port 1. This failure (i.e., the loss of one output signal from port 3) that should only affect 25 percent of the customers, actually affects 100 percent of the customers.
Each of the aforementioned options suffer problems because they are hardware intensive and require additional maintenance and equipment expenditures. Further, the added hardware and resulting connections increase the introduction of insertion losses to the cable lines and ultimately, result in greater signal degradation for the end users. In addition, the system, as a whole, operates with less efficiency and with potentially greater stress on the system's power supply modules.
There is therefore, a need for a solution that allows a video distribution system to operate more efficiently with a minimal risk of insertion loss introduced into the system. The solution should provide a video signal distribution system that can effectively distribute power RF signals converted from an optical source signal, and low frequency electrical signals required to operate downstream devices within the system. It is also desirable that the solution and a resulting distribution system not incur unnecessary hardware or maintenance expenses.